Apparatus for hot dip coating of metals



Oct. 26, 1943. F. J. AHERN ,33

APPARATUS FOR HOT DIE COATING OF METALS Filed Nov. 8, 1939 IN VENT OR.FRANK J AHERN ATTORNEYS.

Patented Oct. 26, 1943 OF METAL Frank J. Ahern, Mentor-on-the-Lake, OhioApplication November 8, 1939, Serial No. 303,457

Claims.

'l'his invention, as indicated, relates to an apparatus for hot dipcoating of metals, particularly ferrous metal sheets or strips in acontinuous process whereby such metal is drawn through a bath of thecoating metal and removed therefrom witha predetermined thicknessofcoating thereon, and adapted for use directly or after furtherfabricating steps for various purposes.

of industry. The invention includes the use of a fum'ace for heating thecoating metal wherein a non-oxidizing atmosphere is maintained above thecoating area and over the coated ferrous strip throughout its period ofcoating and until after it has been cooled tonormal temperature. Ifheinvention also includes the use of a flux in connection with a ferrousmetal material operated on. 'I'heinvention also includes the control ofa-suitable gaseous atmosphere to the end that a non-oxidizing atmospheremay be kept'above the coating area continuously. It also includes theuse of a'protective gas in jet form so as to mechanically break thesurface'tensionof the coating metal adhering to the emerging materialunder-treatment and remove such excess material purely through thepressure exerted by suchgas jet and return the same to the metal coatingbath. It also includes the provision of an angular pathway for theemergence of the treated material from the coating bath whereby theaction of'the gaseous jet referred to above may be assisted through theaction of gravity upon the excess metal which will be caused to flowback into the tank. The invention also includes the provision of a watertrap over the exit passageway for the material so that the gaseousatmosphere supplied to the metal coating furnace and the conduit leadingtherefrom may be maintained free from ingress of air throughout theoperation of the process.

. The principal object of the present inventionis to provide anapparatus for the coating of strip and sheet material, particularly of aferrous char- Another object of the invention is to provide an apparatusfor treating strip andsheet material,.particuiar1y of a ferrouscharacter, so as'to provide thereon a protective coating having a highdegree of adherence to the metal base and particularly of a ferrouscharacter, wherein a coating furnace is utilized in which a protective Iatmosphere is provided over a. coating area which may be partly'insidethe furnace and partly in a passageway leading angularly out of thefurnace whereby material may pass continuously through such coating bathand be free of danger; of oxidation at all stages of its passage throughand out of the furnace.

Another object of the invention is the provision of a mechanism for theapplication of an inert gas to the metal under treatment at a pressureratio preferably sufliclent to break the surface tension. of anyadhering metal globules.

Another object of the invention is to provide an outlet passageway forthe metal undergoing treatment at an angle which is favorable to theciently inclined to return metal in excess of the predetermined amountdesired to the furnace through the force of gravity, which, as stated,may be assisted by a jet reacting against the surface of the coatingmetal to return any excess metal to the coating bath.

A further object of the invention is to provide a coating bath whereinthe inlet and outlet passagewaysare positioned beneath the surface ofthe coating metal bath, and wherein the outlet passageway is of arcuateshape with its free end immersed in a water sealing bath with anintermediate gaseous non-oxidizing atmosphere between the, coatingfurnace and such water sealappear in the course of the followingdescription.

*To the accomplishment of the foregoing and related ends, saidinvention, then, consists of the means hereinafter fully described andparticu-,

larly pointed out in the claims, the annexed drawing and the following,description setting forth in detail certain structures embodying theinvention, such disclosed means constituting,

adapted for productionat a relatively high rate of speed. i

Another object of the invention is to provide an apparatus for coatingmetal strips and sheets,

' however, but several of various formsin which the principle of theinvention may be used.

In said annexeddrawing: Fig. 1 is a diagrammatic side elevation, partlyin section, showingan apparatus embodying the principles of theinvention;

Fig. 2 is a plan view of the structure shown in Fig. 1;

Fig. 3 is a fragmentary sideelevation having a portion cut awayillustrating a modified form of construction embodying invention; and vthe principles of the the metal within the melting chamber.

Fig. 4 is a perspective view illustrating the operative units shown inFigs. 2 and 3 as connected with a gas supply and drive apparatus.

While the application of the coating metal to the base metal strip orsheet has been referred to as a coating, it is to be understood that amore than superficial coating is produced, the adherence of the appliedprotective metal to the base metal being in the nature of a very firmbond which will withstand rolling and various types of heat treatmentwithout injury or causing any flaking or separation whatsoever, andhereinafter when the term coating is used it is to be understood thatthe formation of a. close integral bond, between the coating metal andthe metal being under treatment, is substantially in view.

As is clearly shown in Figure lwof the drawing the apparatus comprises afurnace l for holding a coating metal bath, wherein a reservoir 2 forcoating metals, such as copper, alloys, or any other suitable protectionmetal is maintained through heat applied through burners at the base ofthe furnace, orthrough electrical heating, or any other preferredmanner. The metal bath within the furnace is providedon one side with aninlet passageway 3 inclined downwardly, the lower end being immersedbeneath the level of Opposite the inlet passageway, and in alignmenttherewith an outlet passageway 4 is provided, such passageway having oneend within the furnace chamber beneath the level of the metal coatingbath, and such outlet passageway being inclined upwardly and thendownwardly somewhat in the manner of a syphon. The downwardly inclinedouter end 5 of the outlet passageway is preferably immersed beneath asealing bath which, for the material herein described, may comprise awater bath 6. The water bath, in addition to scaling the outletpassageway, will serve as a cooling medium to reduce the temperature ofthe strip or sheet of metal undergoing treatment to normal temperatureand readiness for such furtherv fabricating process as may be in view.Within the outlet coating area and arcuate central portion I of theoutlet passageway an atmosphere ofanon-oxidizing or of a reducingcharacter is maintained through the supplying of a non-oxidizing gas,which may be nitrogen or the like, from a reservoir, or other source 8,through a passageway 9.

The passageway may communicate with a perforated T-outlet l0 having aplurality of orifices H directed to discharge jets against the strip ofmaterial l2 passing upwardly through the passageway. The upward angle ofthe downward passageway is preferably such that a gentle flow metal willtake place in a return toward the coating bath. In orderto preventglobules of adheringmetal from escaping from the bath and marring thecoating applied thereto, the pressure of the'inert gas upon the adjacentcoated surface will be such as to break up any adherence and dislodgeany globules or metal held by surface tension to the newly coatedsurface and'retum of such excess metal to the coating bath. Any suitablemeans may be utilized for providing the inert or non-oxidizing gasutilized to maintain a satisfactory bond upon the metal undergoingtreatment, but in every instance such gas must be supplied to the outerpassageway under somewhat more than atmospheric pressure in order toprevent backward flow of the sealing liquid into the furnace.

When the operations are carried on on an extended scale it is possibleto dispense with the sealing bath and its cooling function bylengthening the outlet passageway 20 to such an extent that the heatlosses will be adequate by the time the material emerges to prevent anydeterioration of the product through oxidation. In such instances alarger quantity of inert gaseous atmosphere, such as nitrogen and thelike, will have to be utilized to prevent access of air to the outletpassageway to a point where unfavorable action upon the metal undergoingtreatment could take place. The metal stock undergoing treatment may bein the form of coils of strip steel or the rlike held upon reels I2, andthen passed between suitable feed rollers 13, I4 into the bath, andthence carried through the passageways 3, 4 to rollers l5, l6, withinthe cooling bath, and thence to a reel IT for the finished material. Asuitable pump is may be utilized to supply adequate pressure to theinert gas to maintain the arcuate portion of the outlet passagewaycompletely 'filled with such gas at all times.

The metal strip entering the bath should be thoroughly clean and fr e ofan oxide coating. However, to insure the removal of all oxides andforeign matter it is desirable to treat the surface of the metalentering the bath with suitable scavenging and cleansing agents whichmay be in the form of a flux of a pulverized, liquid, or gaseouscharacter. By applying such flux from a source of supply l9, immediatelybelow the feed rollers l3, M, the metal about to be coated enters theinlet passageway fully conditioned to have its surface reacted on by themetal of the coating bath and the formation of a bond of very durableand dependable character with such coating metal.

The flux used may be any of th conventional flux used in removing oxidecoating from ferrous material. A pulverized flux, such as borax has beenfound to operate satisfactorily on thin sheet material but otherscavenging and flux materials may be used, as desired. While the useof.the inlet passageway ha been found advantageous to insure evenrunning of the material thr0ugh the metal coating bath, it is to beunderstood that for some types of material it may be desired to feed themetal to be coated directly into the metal coating bath without the useof a separate inlet passageway. In such event suitable provision, suchas rollers and the like within or adjacent the outlet passageway may beprovided to insure satisfactory coating of the metal under treatment.

Other modes of applying theprinciple of my invention may be employedinstead of those,.ex plained, change being made as regards the structureand method herein disclosed, provided the means and steps stated by anyof the following claims or the equivalent of such stated means beemployed.

I therefore particularly point out and claim as my invention:

1.. An apparatus of the character described having in combination afurnace chamber having a bath of molten metal for coating purposes, aninlet passageway for'metal to be coated entering such furnace chamber ata downwardly inclined angle with the inner end portion of suchpassageway immersed beneath the surface of such coating metal bath, anoutlet passageway for the metal to be coated positioned at an upwardlyinclined angle and having one end immersed beneath the coating bath, andhaving an interdistinctly angle with the inner endportion of suchpassageway immersed beneath the surface of such coating metal bath, anoutlet passageway for the metal to be coated positioned at an upwardlyinclined angle and having one and immersed be neath the coating bath,and having an intermediate arcuatevportion with a downwardly inclinedouter end immersed in a liquid sealing bath, a reservoir for anon-oxidizing gas and a jet manifold outlet and pressure controllingmeans associated therewith and communicating with the arcuate portion ofsaid outlet passageway at a point above atmospheric pressure to forceexcess coating metal back into the bath.

3. An apparatus of the character described having in combination afurnace chamber having a bath of molten metal for coating purposes, aninlet passageway for metal to be coated entering such furnace chamber ata downwardly inclined angle with the inner end portion of suchpassageway immersed beneath the surface of such coating metal bath, fluxapplying means positioned adjacent the outer end of said inletpassageway, an outlet passageway for the metal to be coated positionedat an upwardly inclined angle and having one end immersed beneath thecoating bath, and means including a jet manifold outlet to supplyand'maintain a non-oxidizing gas of a low temperature in 'the 'goutletpassageway over the metal undergoing coating until the metal has reacheda non-oxidizing temperature.

4. An apparatus of the character described having in combination afurnace chamber having a bath of molten metal for coating purposes, aninlet passageway for metal to be coated entering such furnace chamber ata downwardly inclined angle with the inner endportion of such passagewayimmersed beneath the surface of such coating metal bath, an outletpassageway for the metal to be coated-positioned at an upwardly inclinedangle and having one end immersed beneath the coating bath, and havingan intermediate arcuate portion with a downwardly inclined outer endimmersed in a'liquid bath, and means including a jet communicating withthe arcuate portion of such outlet passageway under pressure adequate tomechanically disrupt surface tension of excess coating material upon theWork within such outlet passageway.

5. An apparatus of the character described having in combination afurnace chamber having a bath of molten metal for coating purposes, fluxapplying hopper and outlet means positioned adjacent the line of travelof the metal to be coated temperature. FRANK. J. AHERN.

